Brush for dynamo-electric machines



y 1935- A. BEMIS ET AL 2,041,895

BRUSH F OR DYNAMO-ELECTRIC MACHINES Filed April 4, 1934 Chew/m2 Mfr/9L INVENTOR flrf/rur 5. Bem/s l/arcl' 5. May

AT ORNEY Y Patented May 26, 1936 UNITED STATES PATENT OFFIQE BRUSH FOR DYNAMO-ELECTRIC' v MACHINES Application April 4, 1934, Serial No. 718,936

7 Claims.

This invention relates to brushes for commutators and slip rings of dynamo electric machines and other devices where a carbon member movably contacts with a metal member with passage of electric current therebetween.

An object of the invention is to produce a brush for dynamo electric machines in which the body of one kind of brush forming material has embedded therein relatively coarse particles of another kind of brush forming materials.

Another object of the invention is to produce a brush for dynamo electric machines consisting of coarse particles of carbon having one film forming characteristic embedded in a body of another film forming characteristic.

A further object of the invention is to produce a brush for dynamo electric machines consisting of coarse particles of natural graphite embedded in a body of artificial graphite.

Another object is to produce a brushfor dynamo electric machines consisting of coarse particles of graphite embedded in a body of conducting metal.

The single figure of the drawing illustrates a brush containing the invention.

Brushes for dynamo electric machines are made of various materials including amorphous carbon, artificial or electrically produced graphite, natural graphite or mixtures of graphite and metal powders such as copper, tin, lead, zinc and their alloys.

It is generally known that electrically baked or graphitized brushes having a lampblack base frequently produce a dark coloration of the commutator surface on which they are used. and that such brushes also cut fine grooves around the commutator. This is called threading by brush engineers and is quite prevalent on large motors and generators when underloaded. Threading, however, also occurs on many dynamo electric machines carrying normal loads or overloads.

To improve the operation of such brushes it has been common practice to include with the usual type of brush enough cleaning brushes to sweep across the entire axial length of the commutator segments during one revolution of the commutator. Cleaning brushes are commonly made of some natural graphite material containing an appreciable amount of ash which acts as a polishing agent.

There are a number of objections to the use of two or more kinds of brushes on a generator or motor. In the first place, the user objects to the stocking of an extra kind of brush. Again the conductance of one type of brush is usually inferior.

different from the other, which results in unequal distribution of current with consequent increased rates of wear on the brushes having the greater electrical conductivity. Lastl the user regards the recommendation of two types of 5- brushes for one machine as an admission by the manufacturer that the type normally used is There is therefore considerable opposition to overcome in seeking to improve commutation through the sale of two types of brushes 10 for one machine.

It has been generally thought that the reason so-called cleaner brushes improved the operation when used with electrically baked lampblack brushes was because of the abrasive action of 15 the ash in the former. It was therefore thought that the cleaner brush material could not be molded with the lampblack material to form a single brush for accomplishing the result of the two types for the reason that the electrical baking 20 to which the lampblack brushes are subjected would vaporize the ash content that was supposed to secure the cleaner results. Accordingly, no one attempted to make such a composite type of brush. 25

Upon extensive study we have found that the beneficial action was not due to the scouring property of the ash in the cleaners but was due to the fact that the cleaner brushes and the lampblack brushes tended to produce diifer- 30 ent surface films on the commutators or on the brush faces or on both and that the resultant film was of a superior nature.

To provide a brush to overcome the disadvantages in the brushes of the prior art we mixed 5 the two materials in one and the same brush. This was feasible as the electrical baking to graphitizing temperatures could not injure the action regardless of the vaporization of the ash of the cleaner material.

The cleaner material could not be mixed in the usual fine condition with the lampblack mix as the fine graphite would be disseminated through the lampblack part or? the resulting brush. To overcome this difiiculty we used rela- 45 tively large size graphite spots interspersed in the lampblack brush so that there would be suilicient surface of the graphite material to produce the same type of beneficial resultant film as formerly obtained by the use of cleaner 50 brushes when used with the graphitized lampblack brushes. To accomplish the desired result we foundthat the graphite of the cleaner material should have a relatively large size as compared to the size of mix or graphite particles commonly used in cleaner brushes. Because of their size these graphite particles appear as spots in the surrounding lampblack material. Our invention is not to be limited to any exact size of the graphite spots but by experiment we found that when they were of a size that would pass a mesh screen and stay on a 40 mesh screen they could be mixed with the lampblack material and the one brush resulting therefrom secured all the beneficial results of the two separate brushes regardless of any vaporization of the ash in the high temperature baking.

The lampblack mix may be made in the usual way, for example, by hot mixing it with a binder such as coal tar pitch. After cooling, the resulting mass may be milled to the desired fineness usually through 60 mesh.

To make the graphite spots we prefer to mill graphite, either natural or artificial, 95% through 200 mesh and then hot mix it with a binder, for example, coal tar pitch in the proportion of about 4 parts of graphite to 1 part of pitch but the proportion may be varied to a considerable extent. On cooling, the mass is milled through 20 mesh and onto 40 mesh to produce the graphite spots. The lampblack brush mix above described is then mixed carefully with the spots which are essentially graphite and molded and electrically baked to high temperature. ical and we have secured good results with 2% to 10% of the spots and 98% to 90% of the lampblack brush mix.

We also have produced the graphite spots by molding the graphite spot mix above described to form blocks and then baking these slowly to 1500 F. or even to graphitizing temperatures, after which the resulting material is milled through 20 on 40 mesh and mixed with the lampblack brush mix molded and baked to high temperature as before described.

The invention may be applied also to so-called metal brushes by mixing the graphite spots with metal powder and molding to the desired shape in the usual way.

Referring to the single figure of the drawing, l indicates a brush containing one kind of film forming carbon, for example, graphite spots 2 embedded in a body 3 of another kind of film forming carbon such as graphitized lampblack. This brush, of course, can be of any shape and size and may be made up of other forms of carbon or metal 3 to produce desired results.

It is not even necessary in all cases to use spots of graphite. In some cases the spots may be one kind of amorphous carbon in a body of another form of carbon either amorphous or The proportion is not critgraphite. The spots may be good conducting metal distributed through a metal or carbonaceous body or a mixture of the same. The basic idea of the invention is the use of coarse particles of one type of carbon or other suitable material embedded in a body of another type of brush material so as to produce a desired change in the basic brush without otherwise seriously affecting its properties.

While I have disclosed particular proportions and combinations these are by way of example only, and various departures may be made therefrom. The invention is therefore not to be limited to the materials and proportions or the process set forth.

Having described our claim is:

1. A brush for dynamo electric machines, con sisting of through twenty and on forty mesh particles of carbon of one film forming characteristic embedded in a body of carbon of another film forming characteristic.

2. A brush for dynamo electric machines consisting of through twenty and on forty mesh particles of graphite embedded in a body of another brush forming material.

3. A brush for dynamo electric machines consisting of through twenty and on forty mesh particles of graphite embedded in a body of another kind of carbon.-

4. A brush for dynamo electric machines containing coarse particles of graphite and a carbon matrix and a binder holding said particles and carbon matrix together, said coarse particles consisting of finer particles of graphite held together by a binder other than the first mentioned binder.

5. In brushes for dynamo electric machines containing coarse particles of graphite through twenty mesh and on forty mesh and a carbon matrix and a binder holding said particles and carbon matrix together, said coarse particles consisting of finer particles of graphite held together by a binder other than the first mentioned binder.

6. A brush for dynamo electric machines containing coarse particles of graphite embedded in a body the greater part of which is good conducting metal, said particles consisting of finer particles of graphite held together by a binder.

7. A brush for dynamo electric machines containing coarse particles of graphite through twenty mesh and on forty mesh embedded in a body the greater part of which is good conducting metal, said particles consisting of finer particles of graphite held together by a binder.

ARTHUR S. BEMIS. MILLARD S. MAY.

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